Similarities Between Up Milling and Down Milling

If you haven’t heard about milling, it’s a process that involves removing material from a workpiece using rotary cutters. It is basically cutting metals or making them into specific shapes using a special machine. The two most common and basic milling operations are plain milling and end milling. Milling processes can be further divided into up milling and down milling. Up milling produces a chip that gets thicker and the chip gets thinner in down milling. While there are significant differences between the two milling operations, the two also share some commonalities. In this article, we look at some important similarities between up milling and down milling that are worth considering.

What is Up Milling?

Up milling is a conventional milling process wherein the tool rotates against the direction in which the workpiece is fed. This means the cutting edge of the tool engages the workpiece at the lower end and gradually works its way up, opposing the feed direction. This is the reason conventional milling is also known as up milling. The chip is thicker when the cutting edge leaves the contour, forcing tool pressure at the contour.  In simple terms, the workpiece moves toward the cutter while opposing the direction of rotation. This method is usually not preferred for milling.

What is Down milling?

Down milling, also known as climb milling, is the process wherein the cutter rotates in the same direction as the feed, cutting with the feed direction. The motion of the cutter is in the same direction as the feed motion in down milling. The cutting edge starts at the upper end of the workpiece and moves down. The tool tends to push down toward the table. For this reason, this process is called down milling. This is typically preferred for CNC contour milling 

Key Similarities between Up Milling and Down Milling

Same Cutter Geometry

– Both up milling and down milling are common milling processes that involve using a rotary cutter to remove material from the workpiece. The cutter rotates against the direction of feed in up milling, while it rotates in the same direction of feed in case of down milling operations. However, the geometry of the cutter remains the same in both processes. This results in the creation of various shapes and features.

Similar Cutting Force

– The primary objective is material removal in both processes. The rotating tool gradually cuts the material to achieve the desired shape or dimension. The cutting force is highest at the beginning and it gradually decreases as cutting progresses. This cutting force is the force that is applied to the cutter while cutting the workpiece. Up milling and down milling have similar cutting forces but different directions.

Same Maximum Chip Load

– The maximum chip load is the same in both up milling and down milling if feed per tooth remains constant. The chip load is the material removed by each cutter tooth and the maximum chip load is the limit before the cutter starts to break. It is proportional to the specified feed per tooth. The overall volume of material removed for both milling operations is the same. This is because the same amount of material gets removed in each tooth engagement.

Same Machine Tools

– Both up milling and down milling can be performed using a variety of milling machine tools, such as vertical milling machines, horizontal milling machines, CNC machining centers, etc. The selection of the appropriate machine depends on the specific milling operation and workpiece requirements. In addition to these common machine tools, there are also some specialized machine tools used for both processes. The choice of machine tool also depends on the size and complexity of the workpiece.

Summary

In a nutshell, both up and down milling are two similar milling processes that have their fair share of pros and cons. Despite the similarities, they are quite different on the grounds of chip disposal, surface finish, etc. One of the major advantages of up milling is that tool wear is not affected by the surface condition of the workpiece. One of the many advantages of down milling includes a surface finish that is not affected by the built-up edge if one is created on the cutting edge. While up milling process is generally used for roughing whereas down milling is preferred for finishing purposes.

FAQs

Is down milling better than up milling?

Up milling’s force opposes the feed direction, while down milling’s force goes in the same direction as the feed. In up milling, the tool wear is not affected by the surface condition of the workpiece. 

What is the difference between upcut and downcut milling?

Upcut milling and downcut milling are essentially synonymous with up milling and down milling, respectively. In upcut milling, the cutter rotates against the feed direction, while the cutter rotates in the same direction as the feed in down milling.

What are the advantages of down milling over up milling?

Advantages of down milling include reduced cutting forces, less heat generation, smoother surface finishes, and a reduced tendency to have tool marks on the part. The cutter engages with the workpiece in the same direction as the feed. This makes it preferable for finishing operations and machining delicate materials.

What is the golden rule of milling?

The golden rule of milling is to always use climb milling (down milling) when possible. However, it’s advisable to choose up milling only when the climb milling process is not feasible or could cause issues like workpiece lifting or chatter.

Why is down milling preferred?

Down milling is preferred for several reasons: it generates less cutting force, resulting in reduced tool wear and less power consumption. It also produces a smoother surface finish, which is beneficial for finishing operations.